Hierarchical nickel–cobalt sulfide/niobium pentoxide decorated green carbon spheres toward efficient energy storage

Abstract

Progression in the renewable energy field is tied to the development of high-performance energy storage devices with superior power and energy densities. Herein, an innovative material design was employed to prepare binder-free nickel-cobalt sulfide (NCS) on niobium pentoxide (Nb₂O₅)-decorated carbon spheres (CSs). Initially, CSs were directly grown on nickel foam (NF) via a hydrothermal carbonization approach. Core/shell-like NCS@Nb₂O₅@CS-NF was then synthesized through a hydrothermal process, followed by an electrodeposition process. When employed as an electrode material, NCS@Nb₂O₅@CS-NF achieved an excellent volumetric capacity of 9300 C L⁻¹ at a current density of 18 A L⁻¹. Later, an asymmetric supercapacitor (ASC) was assembled using hydrothermally synthesized CSs as the negative electrode and NCS@Nb₂O₅@CS-NF as the positive electrode. Benefiting from a wide potential window (1.7 V in an aqueous electrolyte), the assembled ASC delivered a remarkable energy density of 410.4 W h L ⁻¹ and a high power density of 29.77 kW L⁻¹. Given the merit of outstanding capacitive performance, the fabricated electrode seems to be a prospective candidate for utilization in renewable energy storages devices.